Methods for forming three-dimensional memory device without conductor residual caused by dishing

Abstract

Embodiments of three-dimensional (3D) memory devices and methods for forming the same are disclosed. In an example, a method for forming a 3D memory device is disclosed. A channel structure extending vertically through a dielectric stack including interleaved sacrificial layers and dielectric layers is formed above a substrate. A dummy channel structure extending vertically through the dielectric stack is formed. An elevating dielectric layer is formed on a dummy dielectric layer. A slit opening extending vertically through the elevating dielectric layer, dummy dielectric layer, and dielectric stack is formed. A memory stack including interleaved conductor layers and the dielectric layers is formed above the substrate by gate replacement. A source contact is formed in the slit opening by depositing a source conductor layer on the elevating dielectric layer and in the slit opening. The source conductor layer on the elevating dielectric layer and at least a part of the elevating dielectric layer are removed.

What is claimed is: 
     
       1. A method for forming a three-dimensional (3D) memory device, comprising:
 forming a channel structure extending vertically through a dielectric stack comprising interleaved sacrificial layers and dielectric layers above a substrate; 
 forming a dummy channel structure extending vertically through the dielectric stack by depositing a dummy dielectric layer on the dielectric stack and in a dummy channel hole; 
 forming an elevating dielectric layer on the dummy dielectric layer; 
 forming a slit opening extending vertically through the elevating dielectric layer, the dummy dielectric layer, and the dielectric stack; 
 forming a memory stack comprising interleaved conductor layers and the dielectric layers above the substrate by replacing, through the slit opening, the sacrificial layers with the conductor layers; 
 forming a source contact in the slit opening by depositing a source conductor layer on the elevating dielectric layer and in the slit opening; and 
 removing the source conductor layer on the elevating dielectric layer and at least a part of the elevating dielectric layer. 
 
     
     
       2. The method of  claim 1 , wherein a thickness of the elevating dielectric layer is not less than 100 nm. 
     
     
       3. The method of  claim 2 , wherein the thickness of the elevating dielectric layer is between 100 nm and 300 nm. 
     
     
       4. The method of  claim 1 , wherein the elevating dielectric layer comprises silicon oxide. 
     
     
       5. The method of  claim 1 , wherein the elevating dielectric layer and the dummy dielectric layer comprise a same dielectric material. 
     
     
       6. The method of  claim 1 , wherein forming the elevating dielectric layer comprises spin-coating a spin-on dielectric (SOD) on the dummy dielectric layer. 
     
     
       7. The method of  claim 1 , wherein removing the source conductor layer on the elevating dielectric layer and the at least a part of the elevating dielectric layer comprises:
 removing at least a part of the source conductor layer to expose the underneath elevating dielectric layer by planarizing the source conductor layer; 
 removing at least a part of the elevating dielectric layer by etching the elevating dielectric layer; and 
 removing the remaining part of the source conductor layer by planarizing the source conductor layer. 
 
     
     
       8. The method of  claim 7 , wherein the planarizing comprises chemical mechanical polishing (CMP), and the etching comprises wet etching. 
     
     
       9. The method of  claim 1 , further comprising:
 prior to forming the dummy channel structure, forming a staircase structure at one edge of the dielectric stack; and 
 after removing the source conductor layer on the elevating dielectric layer and the at least a part of the elevating dielectric layer, forming a word line contact extending vertically through the remaining part of the elevating dielectric layer and the dummy dielectric layer to contact one of the conductor layers in the staircase structure. 
 
     
     
       10. The method of  claim 9 , wherein after forming the memory stack, dishing occurs at a part of the elevating dielectric layer and the dummy dielectric layer right above the staircase structure, and a top surface of the part of the elevating dielectric layer right above the staircase structure is above a top surface of another part of the dummy dielectric layer outside the staircase structure. 
     
     
       11. The method of  claim 1 , wherein forming the source contact comprises, prior to depositing the source conductor layer, forming a lower portion of the source contact by depositing polysilicon into the slit opening. 
     
     
       12. A method for forming a three-dimensional (3D) memory device, comprising:
 forming a channel structure and a dummy channel structure each extending vertically through a dielectric stack comprising interleaved sacrificial layers and dielectric layers above a substrate; 
 forming an elevating dielectric layer above the dielectric stack, wherein a thickness of the elevating dielectric layer is not less than 100 nm; 
 forming a slit opening extending vertically through the elevating dielectric layer and the dielectric stack; 
 forming a memory stack comprising interleaved conductor layers and the dielectric layers above the substrate by replacing, through the slit opening, the sacrificial layers with the conductor layers, wherein the memory stack comprises a staircase structure at one edge of the memory stack; 
 forming a source contact in the slit opening by depositing a source conductor layer on the elevating dielectric layer and in the slit opening; 
 removing the source conductor layer on the elevating dielectric layer and a part of the elevating dielectric layer; and 
 forming a word line contact extending vertically through the remaining part of the elevating dielectric layer to contact one of the conductor layers in the staircase structure of the memory stack. 
 
     
     
       13. The method of  claim 12 , wherein the elevating dielectric layer comprises silicon oxide. 
     
     
       14. The method of  claim 12 , wherein removing the source conductor layer on the elevating dielectric layer and the part of the elevating dielectric layer comprises:
 removing at least a part of the source conductor layer to expose the underneath elevating dielectric layer by planarizing the source conductor layer; 
 removing at least a part of the elevating dielectric layer by etching the elevating dielectric layer; and 
 removing the remaining part of the source conductor layer by planarizing the source conductor layer. 
 
     
     
       15. The method of  claim 12 , wherein forming the source contact comprises, prior to depositing the source conductor layer, forming a lower portion of the source contact by depositing polysilicon into the slit opening. 
     
     
       16. The method of  claim 12 , wherein the thickness of the elevating dielectric layer is between 100 nm and 300 nm. 
     
     
       17. The method of  claim 12 , wherein the forming the elevating dielectric layer comprises spin-coating a spin-on dielectric (SOD). 
     
     
       18. The method of  claim 14 , wherein the planarizing comprises chemical mechanical polishing (CMP), and the etching comprises wet etching. 
     
     
       19. The method of  claim 12 , wherein the forming the dummy channel structure comprises depositing a dummy dielectric layer on the dielectric stack and in a dummy channel hole. 
     
     
       20. The method of  claim 19 , wherein the elevating dielectric layer and the dummy dielectric layer comprise a same dielectric material.